Beauty-wise, she wore her brunette hair down in loose waves, while a smokey eye and natural lipstick completed her look. The Duchess paired the design with blue shoes.
In her Commonwealth Day message, which is printed in the event's order of service, the Queen praised the "Commonwealth connection" that allows people from different nations to bond and celebrate "diversity".
Organised by the Royal Commonwealth Society, the Commonwealth service is the largest annual inter-faith gathering in the United Kingdom and will be broadcast live by the BBC. While we have to admit it's definitely much more exciting dreamily anticipating Markle's princess-worthy wedding dress, Harry's wedding day garb shouldn't be overlooked.
Her father, Thomas Markle, is also said to be unhappy with Prince Harry's comments about the royals being like the "family she never had". The theme of this year's service is "Towards a Common Future", which "emphasizes how the Commonwealth can address global challenges and work to create a better future for all citizens through sub-themes of sustainability, safety, prosperity and fairness", the Palace previously said in a statement.
The Queen became head of the Commonwealth at the age of 26.
Elizabeth has been head of the Commonwealth since 1952 and aides say she regards the success of the organization, which now has 53 members representing over 2.4 billion people, as one of her greatest achievements as queen.
Next month, Commonwealth will be kicking off it's Commonwealth Games on Australia's Gold Coast, beginning April 4.
Prince Harry's American fiancée Meghan Markle on Monday took part in her first official royal engagement with Britain's Queen Elizabeth since the couple announced they were getting married a year ago.
For more from the Royals, watch the clip below!